IC: Forbid inner classes inside inline classes

#KT-43067 Fixed

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -362,6 +362,7 @@ public interface Errors {
     DiagnosticFactory0<KtTypeReference> INLINE_CLASS_CANNOT_BE_RECURSIVE = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory1<PsiElement, String> RESERVED_MEMBER_INSIDE_INLINE_CLASS = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory0<PsiElement> SECONDARY_CONSTRUCTOR_WITH_BODY_INSIDE_INLINE_CLASS = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> INNER_CLASS_INSIDE_INLINE_CLASS = DiagnosticFactory0.create(ERROR);
 
     // Result class
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -717,6 +717,7 @@ public class DefaultErrorMessages {
         MAP.put(INLINE_CLASS_CANNOT_BE_RECURSIVE, "Inline class cannot be recursive");
         MAP.put(RESERVED_MEMBER_INSIDE_INLINE_CLASS, "Member with the name ''{0}'' is reserved for future releases", STRING);
         MAP.put(SECONDARY_CONSTRUCTOR_WITH_BODY_INSIDE_INLINE_CLASS, "Secondary constructors with bodies are reserved for for future releases");
+        MAP.put(INNER_CLASS_INSIDE_INLINE_CLASS, "Inline class cannot have inner classes");
 
         MAP.put(RESULT_CLASS_IN_RETURN_TYPE, "'kotlin.Result' cannot be used as a return type");
         MAP.put(RESULT_CLASS_WITH_NULLABLE_OPERATOR, "Expression of type 'kotlin.Result' cannot be used as a left operand of ''{0}''", STRING);

compiler/frontend/src/org/jetbrains/kotlin/resolve/PlatformConfiguratorBase.kt

@@ -28,6 +28,7 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     SuspendLimitationsChecker,
     InlineClassDeclarationChecker,
     PropertiesWithBackingFieldsInsideInlineClass(),
+    InnerClassInsideInlineClass(),
     AnnotationClassTargetAndRetentionChecker(),
     ReservedMembersAndConstructsForInlineClass(),
     ResultClassInReturnTypeChecker(),

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/InlineClassDeclarationChecker.kt

@@ -124,6 +124,18 @@ class PropertiesWithBackingFieldsInsideInlineClass : DeclarationChecker {
     }
 }
 
+class InnerClassInsideInlineClass : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (declaration !is KtClass) return
+        if (descriptor !is ClassDescriptor) return
+        if (!descriptor.isInner) return
+
+        if (!descriptor.containingDeclaration.isInlineClass()) return
+
+        context.trace.report(Errors.INNER_CLASS_INSIDE_INLINE_CLASS.on(declaration.modifierList!!.getModifier(KtTokens.INNER_KEYWORD)!!))
+    }
+}
+
 class ReservedMembersAndConstructsForInlineClass : DeclarationChecker {
 
     companion object {